1. Field of the Invention
The present invention relates to a charged beam writing technique to write an LSI pattern using a charged beam, particularly to a charged beam writing method and a writing tool configured to correct a beam positional shift on the surface of a substrate to be processed accompanying thermal deformation of a shaping aperture.
2. Description of the Related Art
In recent years, in an electron beam writing tool, a so-called character projection system has been adopted which exposes a character pattern beam formed by a character aperture beforehand to form repeated patterns on a wafer. In this system, a rectangular aperture (opening) is disposed in a first shaping aperture, various pattern apertures (character patterns) are disposed in a second shaping aperture, an image of the first shaping aperture is moved by a beam shaping deflector on the second shaping aperture, and accordingly a desired pattern can be selected. Here, it is assumed that a beam shaped by the character pattern is also categorized in shaped beam.
Additionally, most of the energy of the electron beam which does not pass through the aperture is absorbed by the second shaping aperture in a state in which the electron beam is applied onto the second shaping aperture. For example, silicon is used in a material of the aperture, and the coefficient of thermal expansion is about 2.4×10−6/K. Even when the material symmetrically expands, but when temperature rises by 40K, the opening positioned apart from a center of the aperture by 1 mm moves by about 100 nm. When a reduction ratio of electron optics is 1/15, a positional shift is about 7 nm on the substrate to be processed, and the positional shift cannot be ignored. In heat inflow during the writing, both position and quantity of heat change with time, and it is therefore difficult to predict movement of an aperture position by the thermal expansion.
In contrast, there has been proposed a method of scanning the electron beam on a mark disposed on a stage for mounting a substrate to thereby measure and correct the positional shift of the beam on the substrate to be processed (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-373856). However, in order to apply the electron beam to the mark on the stage, the stage needs to be moved to thereby retreat the substrate to be processed in such a manner as to prevent the electron beam from being applied to the substrate to be processed. Since the stage movement is much slower than deflection of the electron beam, correction of the positional shift requires a long time. Moreover, when the positional shift is corrected many times during the writing, the above-described mark measuring results in a drop of the serviceability ratio of the tool.
Thus, the beam positional shift on the surface of the substrate to be processed accompanying the thermal deformation of the second shaping aperture has not heretofore been ignorable. When the positional shift is measured using the mark on the stage, the stage needs to be moved greatly, and there has been a problem that much time is required in measurement and the tool serviceability ratio drops.
Therefore, there has been a demand for realization of a charged beam writing method and a writing tool capable of measuring and correcting the shift of the beam applied position on the surface of the substrate to be processed accompanying the thermal deformation of the shaping aperture and capable of contributing to enhancement of the tool serviceability ratio.